I got this from Vanns, they let you select two items to compare:
DENON
Denon AVR4306 Details
With a robust 130 watts for each of its 7 channels and Denon's exclusive Dynamic Discrete Surround Circuitry, the AVR4306 is sure to please. It includes auto setup/room EQ with an included microphone. You can connect portable music players as well as stream audio from a Windows-based PC. It upconverts video to HDMI and is XM Satellite Radio ready.
130 Watts x 7 Channels (8 ohms, 20Hz - 20kHz, 0.05 Percent THD), 170 Watts (6 ohms, 1kHz)
3 HDMI Inputs/1 Output, 3 Sets Component Video Input/2 Output
7 Digital Audio Inputs (5 Optical, 2 Coaxial), 2 Digital Audio Outputs (Optical)
1 Set 8-Channel Analog EXT. Input, 1 Set 8-Channel Analog PRE Output
7 Composite Video Inputs/3 Outputs, 7 S-Video Inputs/3 Outputs
New 32-bit Floating Point DSP
iPod Connection Terminals, USB Terminal
XM Satellite Radio Ready with Optional Connect and Play Antenna
EL Remote Controller for Easy Operation
New DDSC (Dynamic Discrete Surround Circuit) -Digital
AL24 Processing Plus for High Sound Quality
DENON Link, Enabling High-Speed, High-Grade Digital Signal Transmission
1 Set Multi Zone Output, 3 Analog REC Output
Auto Set-Up and Room EQ, with MultEZ from Audyssey
Video Up/Down Conversion Capable of Output to HDMI Port
High-Speed, High-Accuracy 12-Bit/216-MHz Video DAC
RJ-45 Ethernet Port and RS-232C Terminal for External 3rd Party Control Systems
Stabilized, Independent Power Supplies for Each Circuit, Chassis Construction to Suppress Internal/External Vibration
PC Setup And Control
Pure Direct Mode, Pre-Amp with Variable Gain Volume
Configurable Surround Back Amplifiers
3 Source and Zone Capability
Variable Subwoofer Crossover Switching (40/60/80/90/100/110/120/150/200/250 Hz)
Dolby Digital EX, Pro Logic IIx, DTS-ES, DTS 96/24, DTS Neo:6, HDCD
Auto Surround Back Channels ON Function, for Auto-Detection of Supporting Sources
On-Screen Display, Front Panel System Setup Control, System Surround Parameters Lockout
11 Sets Analog Audio Inputs, 3 Sets Analog REC Outputs
Muting Level Settings, 3 User Mode Buttons
Large-Output Power Amp Section and Power Supply Configuration
Dimensions: 17.09" W x 6.73" H x 16.89" D
Weight: 40.81 lbs.
Denon AVR4306 Warranty Details
2 Years Parts and Labor
PIONEER
Pioneer VSX84TXSi Details
This top-of-the-line Pioneer VSX84TXSi Elite home theater receiver takes your breath away; it's THX Select2 certified and XM Satellite Radio ready. Four HDMI inputs, one HDMI output, and dual i.LINK advanced resolution audio interfaces keep your digital content digital from source to screen or speakers through single cables. Pumping out 140 watts to each of seven channels and with Advanced MCACC auto room equalization, you'd better be prepared for powerful home theater experiences.
DTS-ES Discrete, DTS 96/24/NEO:6, Dolby Digital EX/Pro Logic IIx, WMA9 Pro Decoding
140 Watts x 7 Channels (20Hz-20kHz, 8 Ohms, 0.09% THD--FTC)
4 HDMI In/1 Out (1080p/DVD-A Compatible)
Dual i.LINK Audio Interfaces; 2 Coaxial, 4 Optical (1 F/3 R) Digital Audio In; Digital Optical Out (1 F)
8 Multi-Channel Inputs
3 Component Video In/1 Out, 5 S-Video In (1 F/4 R)/2 Out, 7 Composite Video In/2 Out, 4 Audio In/3 Out, Phono In, USB PC In
Sharc EX + 48-Bit Freescale DSP
12 Advanced Surround Modes, Virtual Surround Back Mode
TBC Digital Upconversion Composite/S-Video/Component To HDMI
2 Preset Multi-Operation Learning LCD Remote Controls (Main/Secondary)
Advanced MCACC Auto Room Set-Up/9-Band EQ/3-D Display Via PC
THX Select2 Processing And Certification
XM Satellite Radio Ready (XM-HD With Neural Sound)
192KHz/24-Bit Audio DAC, 96 kHz/24-Bit Video DAC
Direct Energy Amplifier Design/Rigid Trans-Stabilizer Construction
Large Banana Speaker Terminals (L/R/C/LS/RS/SBL/SBR)
iPod Audio/Photo/Video Compatible
Sound Retriever For Enhanced Portable Audio Playback
Faroudja DCDi Video Scaler (480p, 720p, 1080i)
Assignable Surround Back Speaker (Normal/Zone 2/Front Bi-Amp/MR & MS Modes)
AM/FM Audio Tuner With 30 Random Preset Stations
SR+ (Smart Remote) Terminal Output
12 V Trigger, RS-232C Control, IR In/Out
PQLS Provides Jitter-Free Multi-Channel High Resolution Audio (DVD-Audio/SACD)
8-Channel Audio Pre-Output
Multi-Room/Multi-Source Output (3 Zone)
Dialog Enhancement, Headphone Output, Midnight Listening Mode
X-Curve Compensation, Hi-Bit Sampling
HDMI/Component/S-Video/Composite Monitor Outputs
On-Screen Display
Dimensions: 16.54" W x 7.36" H x 18.35" D
Weight: 35.3 lbs
Pioneer VSX84TXSi Warranty Details
Two-Year Parts And Labor Warranty
From this I also found the Pioneer has a 48-bit DSP vs. Denon 32-bit. Also, the Pioneer seems to have 24-bit DAC vs. Denon 12-bit DAC.
This is not looking too favorable for the Denon.